[TedTimmons]

For my RV-6 the aerobatic weight is 1,375 lbs. I have calculated the equivalent G limit at other weights as follows and would like to know if my reasoning is correct.
Weight G's "G Weight"
1,375 6.0 8,250
1,450 5.7 8,250
1,500 5.5 8,250
1,550 5.3 8,250
1,600 5.2 8,250

My conclusion is that I can pull 5 G's at my max weight of 1,600 lbs and still be within the design specs.

 

[Mel]

Yes

Your reasoning is correct. But I personally wouldn't push it to the limits. I stay within "utility category" limits (4.4Gs) at gross weight.

 

[Geico266]

Welcome to VAF


Is it safe to assume the "weak points" in high "G's" are the spars & engine mounts? Where are the failure / damage points at?

Just curious.

 

[Mel]

Welcome to VAF
Is it safe to assume the "weak points" in high "G's" are the spars & engine mounts? Where are the failure / damage points at?
Just curious.

Only the designer, and sometimes the test pilot know for sure!

 

[szicree]

The Van's -8 demonstrator got overstressed and snapped the wing around midspan. Remember though that our wings are of stressed-skin design, so I'm not sure that you can really say that the spar is the weakness.

 

[Ironflight]

Just remember that gross weight is not based solely on structural loading, and the CG envelope is not always a straight set of datum limits - the forward and aft points can change with Gross weight such that as you get heavier, the envelope gets smaller.

Paul

 

[sjjonesnz]

Given these are design/structural limitations, I assume they're not determined by our flight testing and so must be published somewhere. Can anyone point me to them as I'd like to put them in my PoH.

 

[plehrke]

Loading Conditions

One other thing to keep in mind is that the aerobatic catagory and the utility catagory use different loadings to determine strength margins. In the utility catagory no analysis may be done for a unsymetric max g pull as that is not a manuver used by a utility category aircraft.

 

[flion]

Given these are design/structural limitations, I assume they're not determined by our flight testing and so must be published somewhere. Can anyone point me to them as I'd like to put them in my PoH.

Page 15-21 in my RV-7 manual (old preview plans). Section 15 is Final Inspection and Flight Test. The relevant heading is G-Load Testing.

 

[sjjonesnz]

Thanks for that, but unless I'm missing something I can't see what the max. G-limit is at MAUW (1800lbs) and at weights between that and max aerobatic weight (1600lbs).

Knowing those limits I'll know how much fun I can safely have with my 220+lb friends

 

[flion]

Well, if you ask Van's, none. It is aerobatic solo only (well, ok, two really light people and a splash of fuel ) and you can assume utility category above 1375#, 1600# for you -7 drivers. Utility is +4.4/-1.8G. Specifically, 'For operational gross weights above this figure (max aerobatic gross), aerobatic maneuvers should not be flown.' That section has pretty much all the design information you will get out of Van's. They mention a calculated +9G breaking strength which is 150% of the recommended max G, but they also discourage excursions into that realm. Realistically, I think you'd need a G-suit to have fun over about 3-4G. Anyway, Van's has traditionally been conservative and close-mouthed about their design criteria, probably for good cause. I'm sure they don't want to encourage the kind of hedging that the first post suggests due to the real possibility of litigation. Look at their reaction to the Harmon Rocket. Their stance is understandable if you realize that even tacit approval can lead to settlements in our court system.

The flip side of that is that you are (usually) both the manufacturer and the test pilot. Nothing stops you from declaring a different limit and testing it. And if it works (again, the Rocket) then you win! But if you're wrong, Van's can say they never approved the change.

Sorry, Steve, I'm not trying to be obtuse. Van's has never outright published the non-aerobatic G-limits for anything other than the -9 (and now the 10) that I know of. However, if you do the kind of calculation that Ted did you will get a load well over the next limiting category (at least in the US): utility. So it's been a safe assumption that utility limits are the max when over aerobatic weight. A less conservative approach is what Ted is proposing; instead of a step function from aerobatic to utility loads you get a calculated maximum load which results in a maximum G for any given weight. As Mel points out, it's not that simple. There are load moment considerations, for example. 'Twere me in the seat, I'd err on the side of caution.